Start version 6.2.0

* Add Christian Tzolov to author name in the doc
* Move `whats-new.adoc` content to new `changes-6.0-6.1.adoc`
* Upgrade to Gradle `8.1.1`
* Upgrade to Spring Framework `6.1`
* Fix `StompSessionManagerTests` for deprecated `ConcurrentTaskScheduler` ctor
* Fix XML configs for Kafka to use types for ctor args instead of their names.
Apparently SF doesn't do a discovery by names anymore.

gradle/wrapper/gradle-wrapper.properties

@@ -1,7 +1,7 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionSha256Sum=ff7bf6a86f09b9b2c40bb8f48b25fc19cf2b2664fd1d220cd7ab833ec758d0d7
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.0.2-bin.zip
+distributionSha256Sum=e111cb9948407e26351227dabce49822fb88c37ee72f1d1582a69c68af2e702f
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.1.1-bin.zip
 networkTimeout=10000
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists